1. Field of the Invention
The present invention relates to an electroluminescent polymer and an organic electroluminescent device using the same, and more particularly, to an electroluminescent polymer including a polycyclicamine unit in its polyarylene backbone and an organic electroluminescent device using the same that offers high luminance and efficiency.
2. Description of the Related Art
Since the report of a multi-layered organic electroluminescent device, each layer having a specific function, by C. W. Tang of Eastman Kodak company, due to its advantages of light weight, thinness, a wide range of colors, fast switching speed, and high luminescence at low driving voltage, a lot of research on organic electroluminescent devices has been conducted for the last decade. As a result of this research, great improvements in the performance of organic electroluminescent devices have been made in a short period of time. These improvements include balanced charge injection due to multi-layered structures, color tunability and higher quantum efficiency by doping, etc. In addition, new electrodes formed of specific alloys have been found to be suitable for organic electroluminescent devices.
Such organic electroluminescent devices can be classified according to the molecular weight of their materials and manufacturing processes. Organic electroluminescent devices can be manufactured from low molecular weight compounds and large molecular weight compounds. Low molecular weight compounds can be layered by vacuum deposition and can be easily purified to a high degree. In addition, color pixels can be easily obtained in a low molecular weight device. Despite these advantages of low molecular weight organic electroluminescent devices, they still require further improvements for practical application, for example, in quantum efficiency and color purity, and there is a need to prevent crystallization of thin layers. Various studies on such electroluminescent displays using low molecular weight compounds have been actively undertaken, especially in Japan and the U.S.A. For example, Idemitsu-Kosan Co., Ltd. of Japan first exhibited in 1997 a 10-inch full color organic electroluminescent display using a color-changing medium. Pioneer Corporation of Japan presented a 5-inch passive matrix (PM) full color organic electroluminescent display. Recently, Pioneer Corporation and Motorola Inc. have arrived at an agreement concerning the mass production of cellular phones having organic electroluminescent displays, implying that low molecular weight electroluminescent displays will be commercially viable in the near future.
Research on electroluminescent devices using polymers has been accelerated since the Cambridge Group's report in 1990 on the ability of poly (1,4-phenylene vinylene) (PPV), π-conjugated polymer, to emit light when exposed to electricity. π-conjugated polymers have an alternating structure of single bonds (σ-bonds) and double bonds (π-bonds), where π-electrons are evenly distributed to move freely in the polymer chain. Accordingly, π-conjugated polymers have semiconductor properties and can emit light of a visible range corresponding to the HOMO-LUMO energy bandgap, via proper molecular designing, when applied to an emissive layer of an electroluminescent device. Such a polymer can be easily formed as a thin layer in the manufacture of electroluminescent devices by spin coating or printing, at low costs and has a high glass transition temperature that allows the thin layer to have good mechanical properties. Thus, such polymer-based electroluminescent devices are expected to be more commercially competitive than low molecular weight electroluminescent devices in the near future.
However, electroluminescent devices using polymers have problems of low color purity, high driving voltage, low efficiency, etc. Research has been actively conducted to address the problems of polymer-based electroluminescent devices. As an example, copolymerization (U.S. Pat. No. 6,169,163) or blending (Synthetic Metal, Vol. 106, pp. 115-119, 1999) of a fluorene-containing polymer was suggested for improved electroluminescent properties. However, improvements are still required.